Dyspnea is defined as a shortness of breath or difficult breathing (the subjective feeling of being out of breath) caused by heart or lung disorders, strenuous activity, high anxiety or stress. Dyspnea derives from interactions among multiple physiological, psychological, social, and environmental factors, and may induce secondary physiological and behavioral responses. Dyspnea is different from tachypnea (rapid breathing) and hyperpnea (deep breathing). Tachypnea and hyperpnea can occur with hyperventilation, or over breathing beyond what is required to maintain arterial blood gases within normal limits. Fear or anxiety may create even more distress in dyspneic patients.
Clinically, a dyspnea index has been developed as a monitoring tool for dyspnea. One conventional method of determining a dyspnea index value has a subject take a deep breath in and count out loud from 1 to 15 (should take approximately 8 seconds). When stressed or running out of air, the subject stops counting, takes another deep breath and then continues counting from where they left off. This is repeated as needed until the subject finishes counting to 15. The number of breaths needed to take in addition to the very first one is the dyspnea index.
Using the subject's dyspnea index measurement, a value of 0-1 is considered normal. A dyspnea value of 2-3 is acceptable, depending on what activity is being performed. At a dyspnea value of 4, the subject should slow down, and think about stopping. At a dyspnea value of 5, the subject should definitely stop and rest.
Dyspnea may be classified as chronic, acute, or terminal. Chronic dyspnea has a variable intensity and persistent shortness of breath. This is most often seen in patients with chronic obstructive pulmonary disease (COPD). Acute dyspnea causes episodes of shortness of breath with high intensity. It may be seen in patients who have suffered a myocardial infarction or pulmonary embolism. Terminal dyspnea occurs in patients with end-stage diseases, and these patients may be in a hospital, at home, or in a hospice. This type of dyspnea is a common complaint in patients with cancer. Dyspnea can be caused by a variety of conditions, including metabolic, allergic, psychiatric, and neuromuscular disorders, and by pain. However, cardiac and pulmonary disorders are the most common causes.
To manage dyspnea, nonpharmacological and pharmacological interventions may be performed. For example, treating patients in cardiac failure with digoxin and diuretics may resolve the problem. Stimulation of mechanoreceptors in the respiratory musculature or over the face has reduced dyspnea in some patients. Vibration of the intercostal muscles, in phase with inspiration so that contracting respiratory muscles are vibrated, has relieved dyspnea in some COPD patients. This intervention has worked best with severe dyspnea at rest. Movement of cool air across the face by a fan or an open window can stimulate mechanoreceptors in the face, minimizing mild dyspnea.
Patients with COPD often obtain relief from dyspnea while sifting and leaning forward with their arms supported on a table. Unsupported arm and shoulder movement alters the efficient use of respiratory muscles. This position may also improve overall inspiratory muscle strength and enhance the efficiency of diaphragmatic breathing. Techniques like pursed-lip and diaphragmatic breathing are widely used to reduce dyspnea in COPD patients, though their effect is variable. These breathing techniques allow for slower and deeper breathing, thus raising tidal volume and decreasing respiratory rates. Pursed-lip breathing is especially useful for patients with emphysema because it creates positive end-expiratory pressure in the alveoli, thus splinting airways that have lost their collagen matrix. However, patients often revert to their fast and shallow breathing patterns, which may be compensatory for the mechanism causing dyspnea.
Oxygen, administered by mask or nasal cannula or transtracheally, improves dyspnea. In patients with COPD, most authorities recommend oxygen therapy for raising PaO2 levels to at least 55 mmHg to 60-mmHg or oxygen saturation to 88% to 90%.
Evidence suggests that opioids, despite their possible respiratory depressant effect, are useful in managing dyspnea. While the action of opioids to relieve dyspnea is not fully understood, the drugs may act by blunting the emotional reaction to dyspnea by interaction with opioid receptors in the limbic system. Because opioids cause euphoria, they reduce fear, anxiety, and the associated restlessness and muscle tension that decrease oxygen consumption. Opioids may also relieve dyspnea by action on the chemoreceptors, thus reducing respiratory drive.
When the dyspnea becomes intolerable and increased doses of systemic opioids are contraindicated because of unacceptable adverse effects, nebulized morphine may be started. Nebulized morphine may relieve dyspnea by direct local action on peripheral opioid receptors in the airways so that it does not reach the systemic concentration to the extent that oral, subcutaneous, or intravenous morphine does. Therefore, some patients experience relief of dyspnea with fewer adverse effects.
Anxiolytics frequently used to relieve dyspnea include benzodiazepines and phenothiazines. These act by depressing the hypoxic, hypercapnic response to dyspnea and the emotional response to dyspnea. Depending on the cause of dyspnea, patients may benefit from bronchodilators. Since methylxanthines cause smooth muscle dilation of the airways and improve the contraction of the diaphragm, they may be useful in patients with COPD. Similarly, inhaled beta-2 adrenergic agonists and anticholinergics cause smooth muscle dilation of the airways, thus improving lung mechanics and possibly relieving dyspnea.